In known electro-hydraulic control systems for mineral, e.g. coal, mining installations each roof support along a working is provided with an electronic control unit with all the control units being connected to one another and optionally to a central control station via a data transmission system for the transmission of data (see "Gluckauf" 1981, pages 1155-1162; "Gluckauf" 1984, pages 135-140; "Gluckauf" 1986, pages 543-552; and "Gluckauf" 1986, pages 1183-1187). The integrated control units usually have keyboards with which the various control processes (hydraulic individual control, continuous control at the adjacent supports and optionally sequential control with so-called sliding support groups) can be carried out.
It is necessary to provide electrical power at an intrinsically safe level and in known control systems, each support and therefore each control unit is provided with its own power supply which is optionally integrated with the face lighting circuits. Such decentralized power supply arrangements are distinguished by high reliability but necessitate considerable expense. With the large number of supports normally provided in an extraction operation, the expense is extremely high not only for the power supply system but also for the data transmission system.
A power supply arrangement for electro-hydraulic control systems or other electric loads in mining is known from DE-PS No. 35 38 251, in which a group of electronic control units for switching in electric loads in the form of electromagnetic valves is provided with a common electric power pack which is designed for a maximum current capacity which is smaller than the total current requirement of all loads. In this arrangement, therefore, more electric loads can be connected to the power pack than the power pack can properly supply. Logic comparisons about the number of loads supplied in comparison with the maximum number of loads which can be supplied are carried out in the control units by means of control logic in the electronic control means e.g. microprocessor or microcomputer of the units. This should ensure that, at any moment, the electric power pack is supplying only the maximum number of electric loads that it can supply according to its capacity. Overloading of the power pack is thus avoided but this arrangement is not particularly versatile and it does not respond in a dynamic sense to changing conditions or priorities.
An object of the invention is to provide an improved power supply arrangement.